Make Ahead
Prepare as directed except for baking; cover. Refrigerate up to 24 hours. When ready to serve, bake, covered, at 375°F 40 to 45 min. or until heated through. Remove from oven; uncover. Sprinkle with remaining 1/2 cup cheese. Let stand 5 min. or until cheese is melted.
Substitute
Substitute 1 lb. extra lean ground beef, cooked, drained for the tuna.